Pressurized pumped hydro storage system

ABSTRACT

An energy or water storage system can comprise a storage reservoir, a discharge reservoir, a pump for charging the storage reservoir, and a turbine or similar discharge device. The storage reservoir can comprise a flexible bag covered by overburden that creates pressure inside the bag. Energy is stored by raising the overburden. The bag can comprise a shaped internal filler piece to prevent formation of a crease at the bag edge. Solar panels can be mounted above any bag to make additional use of the land. Solar panels mounted on overburden can have tracking mechanisms and controls suitable to achieve desired orientation regardless of the slope of overburden. Elevation difference between the storage reservoir and discharge reservoir can be used, including an underground cavity. The bag can have internal tethers to influence bag shape.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of Provisional PatentApplication U.S. Ser. No. 62/470,603, filed Mar. 13, 2017, andProvisional Patent Application U.S. Ser. No. 62/470,607, filed Mar. 13,2017, all of which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

There is a general need for energy storage technologies, such as to helpbalance supply and demand in the electric power grid. This need becomesmore prominent with the increasing use of renewable energy sources suchas wind and solar, because the pattern of energy generation from thosesources tends to be irregular in time and not necessarily well matchedto demand.

Currently, the energy storage technology that has by far the largestbase of experience at significant size scales is pumped storage hydro.Conventional pumped storage hydro uses two reservoirs of water atdifferent elevations. However, new sites for pumped storage hydro areoften non-optimal for reasons of topographical location, environmentalsensitivity or significant capital expenditure. It would be desirable toallow the use of pumped storage technology in more locations includingat sites that are not mountainous.

A known effort of this type is published by Olsen as US patentapplication 20110113769, and WO2010003412A2, and also “A new principlefor underground pumped hydroelectric storage,” by Jan Olsen, Journal ofEnergy Storage 2 (2015) 54-63). In this system, hydraulic head iscreated by the weight of soil on top of a deformable bag. The soil has adensity greater than the density of water. When the bag is filled with afluid such as water so as to store energy, the soil on top of the bag islifted upward. For recovery of energy, the fluid such as water isallowed to flow out of the bag as the soil on top of the bag settles toa lower elevation. Energy storage is accomplished using a pump, andenergy recovery is accomplished with a turbine-generator. Similartechnology is described in U.S. Pat. No. 8,950,181 to Ivy et al. Ingeneral, it is desirable to provide further improvements in energystorage by pressurized water stored in bags, including improvementsrelating to bag design and placement.

SUMMARY OF THE INVENTION

An embodiment of the invention can include an energy or water storagesystem comprising: a bag comprising a deformable boundary defining aninterior that can be filled with a fluid and emptied of the fluid asdesired, the bag being capable of occupying a less-filled configurationand a more-filled configuration; a mass of overburden overlying the bag,the mass being able to be raised and lowered as a function of an extentof filling of the interior of the bag, wherein the interior of the bagcomprises an internal filler piece having a longitudinal direction thatat least approximately follows all or at least a portion of an outeredge perimeter of the bag, wherein the internal filler piece has across-sectional shape, the cross-sectional shape being a shape of across-section taken perpendicular to the longitudinal direction, whereinthe cross-sectional shape, at an outer-facing portion of the internalfiller piece, has a curved shape in contact with an interior surface ofthe bag, and the curved shape in contact with the bag interior surfacehas an outer radius of curvature that is at least one bag materialthickness of the bag. Such a bag can also include an internal tether toinfluence the shape of the bag.

An embodiment of the invention can include an energy or water storagesystem comprising: a bag comprising a deformable boundary defining aninterior that can be filled with a fluid and emptied of the fluid asdesired, the bag being capable of occupying a less-filled configurationand a more-filled configuration; a mass of overburden overlying the bag,the mass being able to be raised and lowered as a function of a degreeof filling of the interior of the bag, further comprising a plurality ofsolar energy collectors placed atop the overburden and transmitting atleast some of their weight to the overburden, wherein the system uses atleast some energy produced by the solar collectors and stores the energyby increasing a filling of the bag. The solar energy collectors cancomprise a tracking system and the tracking system can achieve a desiredorientation of the some of the solar energy collectors regardless of alocal orientation of a surface of the overburden at a location of thesome of the solar collectors. There can be tilt or orientation sensorsto which the controls are responsive.

An embodiment of the invention can include a method of creating anenergy or water storage system, the method comprising: placing a storagebag on ground or a prepared substrate; excavating in ground near thestorage bag, producing excavated dirt, wherein at least some of theexcavated dirt is place atop the storage bag; creating a first dischargereservoir in a region that has been excavated; and providing andconnecting a first pump device suitable to pump a liquid from the firstdischarge reservoir into the storage bag, and a first energy recoverydevice suitable to recover energy from passage of the liquid into thefirst discharge reservoir. Such a method can involve creating a seconddischarge reservoir at an elevation different from the elevation of thefirst discharge reservoir. Such reservoirs can be depressions in theearth's surface or an underground cavity.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

Embodiments of the invention are further described in the followingnon-limiting illustrations.

FIG. 1A is a view of an energy storage system.

FIG. 1B is a view of a detail of the bag used in experiments by Olsen.

FIG. 1C shows a bag configuration in which energy is stored.

FIG. 1D shows the same bag in a configuration in which energy isdischarged.

FIG. 2A shows a bag, having a lap joint located away from the edge ofthe bag, in a configuration in which energy is stored.

FIG. 2B shows the same bag in a configuration in which energy isdischarged.

FIG. 3A shows, in cross-section, a bag having an internal filler piece,when the bag is nearly empty.

FIG. 3B shows, in cross-section, a bag having an internal filler piece,when the bag is nearly full.

FIG. 3C shows certain dimensions of an internal filler piece having atapered shape.

FIG. 3D shows certain dimensions of an internal filler piece having ateardrop shape.

FIG. 4A shows a group of solar collectors in which a tracking systemcompensates for changes in the orientation of the surface of theoverburden.

FIG. 4B shows a group of solar collectors with an orientationpreservation system comprising linkages.

FIG. 5A shows relative elevations of a storage bag and a discharge bagand an excavation.

FIG. 5B shows relative elevations of a storage bag and a discharge bagin a situation in which some natural elevation difference is present.

FIG. 5C shows a system in which a discharge reservoir is in anunderground cavity.

FIG. 6A shows a bag, in cross-section, having one internal tether.

FIG. 6B shows a bag, in cross-section, having two internal tethers.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1A, there is shown an energy storage systemcomprising a storage reservoir and a discharge reservoir. The storagereservoir comprises a bag that is filled with fluid (water) and iscovered with a layer of overburden that creates pressure inside the bag.Filling of the bag causes lifting of the overburden and storage ofenergy. Retrieval of energy is accomplished by letting fluid out of thebag through a turbine or similar energy recovery device. As illustrated,the discharge reservoir is an open body of water.

FIG. 1B, from the Olsen reference shows details of the shape of the bagat its edges, as described by Olsen, for the situation where the bag isfull, with the axes being dimensions in meters. In the Olsen journalarticle, the bag placement with respect to earth material is such thatits edge has a downturned shape i.e., the outermost part of the bag veryclose to the edge is nearly vertical, and the joint itself is located inearth that is some distance away from the region of earth that isactively involved in moving during filling and emptying of the bag. Thereport of Olsen's experiments, corresponding to FIG. 1B, indicates thatwhen the bag was full, it was filled to a vertical dimension that isonly several percent of the lateral dimension of the bag. The verticallift distance is a parameter in the economics of such a system, suchthat for a given bag construction, a greater lift distance is believedto improve the economics of the system. In the Ivy reference, theappearance of the edge of Ivy's bag is somewhat different from what isin the Olsen reference, although the Ivy reference does not providegreat detail about the geometry of the edge of the bag or about jointsin the bag. It is further believed that another parameter in improvingthe economics of the system is to increase the thickness (or weight) ofthe layer of overburden.

Referring now to FIG. 1C-1D, there is illustrated one possible design ofthe edge of the bag in embodiments of the invention. This is similar tothe system of Olsen, except that the shape of the substrate is dished soas to allow greater vertical lift distance. In such a design, the bag isillustrated as being formed of two sheets of material that are joinedface-to-face at their edges, forming an upper layer 110 and a lowerlayer 120. When the bag 100 is empty the bag can lay flat withoutcausing any further crease or folding of material at the edges of thebag because of the face-to-face nature of the joint that already existsat the bag edge and defines the bag edge. However, with such a jointdesign, just as in Olsen, the internal pressure inside the bag 100 canact in a way such as to try to separate the joint, i.e., to peel the twosheets away from each other.

Bag Edges Having Continuous Bag Material and Shaped Internal FillerPiece

Referring now to FIGS. 2A-B, for embodiments of the invention, there isillustrated another possible design of the edge of the bag. In such adesign, the bag material is continuous around the edge from uppersurface 110 to lower surface 120 of the bag 100. In FIG. 2A-B there isalso shown a joint, in the form of a lap joint, where two pieces ofmaterial overlap with each other for some distance. As illustrated, thelap joint is located somewhere other than where a crease on the outsideof the bag 100 may be located. In general, such a lap joint could belocated anywhere that may be desired. A system in which the bag materialis continuous around the edge (as in FIG. 2A and FIG. 2B) appears to becapable of somewhat larger vertical dimension increase or lift distance(possibly expressed in proportion to a lateral dimension of the bag),compared to the amount of lift that is reported by Olsen in thesituation of FIG. 1B.

In geometries in which the bag material is continuous from the uppersurface to the lower surface of the bag as in FIG. 2B, it is possiblethat when the bag is empty and overburden is pressing down on the bag, acrease could be formed at the edge of the bag, and the crease could havea fairly small radius of curvature, due to load exerted on the bag fromabove by the overburden 130. Furthermore, when the same bag is full, thecrease can be expected to open up or unfold to a more gentle radius ofcurvature. Such change of local curvature at the edge of the bag couldbe repeated during every charge-discharge cycle. This change of localcurvature has the possibility of damaging or weakening the bag materialin the immediate vicinity of the crease, especially when such motion isrepeated many times. This repeated motion could make the crease locationa potential source of failure of the bag.

Referring now to FIG. 1A and FIG. 3, in an embodiment of the invention,there may be provided an energy storage system 10 comprising a bag 100.The bag 100 may comprise an upper layer 110 and a lower layer 120opposed to the lower layer 110. The bag 100 may be able to contain aninternal pressure. The bag 100 may be at least partially covered with adistributed weight such as a deformable or flowable material, which isoverburden 130, which may be in contact with upper surface of upperlayer 110, and may create an internal pressure inside the bag 100.

Bag 100 may have an outer edge 140. Inside bag 100, there may be aninternal filler piece 200, which may serve to prevent the bag fromforming a sharp crease at the bag outer edge in the bag is nearly emptyand is being pressed upon by overburden. The internal filler piece 200may be located near edge 140 of the bag 100 and may extend along edge140 of bag 100. The internal filler piece 200 may proceed all around thecircumference of bag 100. Accordingly, the internal filler piece 200 mayform a closed loop. For example, it is possible that the overall shapeof the bag 100 may, in plan view, be generally rectangular havingrounded corners. In such a situation, the overall shape of the closedloop of internal filler piece 200 may also be a rounded rectangularsuitable to fit inside the bag 100 close to the outer edge of the bag100. However, it is not essential that the internal filler piece 200 bea closed loop. The internal filler piece 200 could be in segments, orcould be of other form. The internal filler piece 200 could be attachedto the interior of bag 100, perhaps intermittently, or it does not haveto be so attached.

Referring now to FIG. 3A, there is shown (on two opposed sides of thebag, with a central region of the bag broken away for clarity ofillustration), internal filler piece 200 and the bag 100 itself for anearly-empty condition. FIG. 3B shows the same components with the bag100 being in a partially-full condition. It can be seen that in FIG. 3B,in regard to the top or upper layer of the bag, less of the bag is inclose contact with the internal filler piece 200, although the contactof the bottom or lower layer of the bag with the internal filler piece200 remains approximately the same as in FIG. 3A. Referring now to FIG.3C, there are illustrated certain dimensions of the cross-sectionalshape of the internal filler piece 200. the maximum overall horizontaldimension DmaxH, the maximum overall vertical dimension DmaxV, theradius of curvature of the outward-facing curved surface Router, and theradius of curvature of the inward-facing tip Rtip. Referring now to FIG.3D, there is shown an alternate possible shape of the internal fillerpiece 200, which may be described as a teardrop shape. Its dimensionscan be characterized similarly to those of FIG. 3C, but in FIG. 3D thecross-sectional shape also has a gentle concavity between the tip andthe outward-facing curved surface.

The internal filler piece 200 may have a longitudinal direction, or atleast a local longitudinal direction along a portion of its length, andmay have a cross-sectional shape, in a cross-section taken perpendicularto the longitudinal direction of internal filler piece 200. Thecross-sectional shape of internal filler piece 200 may be such that onan outer-facing portion of the internal filler piece 200, the curvedshape that may contact the interior surface of bag 100 may have a radiusof curvature that is at least one bag material thickness of bag 100. Theinternal filler piece 200 may have a maximum external dimension in thevertical direction that is at least one thickness, or at least twothicknesses (two times the bag material thickness), or at least fivethicknesses, of the bag material.

The cross-sectional shape of internal filler piece 200 may have ahorizontal dimension that is greater than its vertical dimension.

The cross-sectional shape of internal filler piece 200 may have asmallest radius of curvature facing away from the bag that is smallerthan the radius of curvature of internal filler piece 200 facing theadjacent bag 100.

The internal filler piece 200 may have a shape that, on itsexternally-facing portion, is an arc of a circle. Internally-facing, theinternal filler piece may have a taper to it. The taper may be a lineartaper or other form of taper.

As illustrated in FIG. 3A-3C, the cross-sectional shape of the internalfiller piece 200 may be entirely convex. The cross-sectional shape maybe circular or may be elliptical or of other entirely convex shape. Asyet another possible shape, the internal filler piece 200 may be convexin some places and concave in other places. An example of such would bea teardrop shape as illustrated in FIG. 3D.

At its innermost edge, the internal filler piece 200 may be somewhatsharp, and yet even a relatively sharp edge can be described by a radiusof curvature. The sharper the edge, the smaller is its radius ofcurvature. The internally facing edge of the internal filler piece 200may have a radius of curvature that is less than the thickness of thebag material, or less than 0.5* the thickness of the bag material (i.e.,half of the thickness of the bag material), or less than 0.2* thethickness of the bag material, or less than 0.1* the thickness of thebag material.

Co-Location with Solar Panels

In an embodiment of the invention, a pressurized pumped storage hydrosystem may be co-located with a solar energy collection system. Solarenergy panels systems such as photovoltaic panels are practical for useon vacant land of moderate or larger size, just as is embodiments of theinvention.

In regard to the storage reservoir, it is possible that solar panels 500may be mounted so as to occupy at least some of the same land area asthe storage reservoir, being located above the storage reservoir. Oneoption is that the solar panels 500 can be mounted on a fixed structurethat is structurally independent of the storage reservoir. Such solarpanels could be fixed, single-axis tracking, or dual-axis tracking, orany other desired configuration.

In regard to the storage reservoir, the storage reservoir could be a bagor a plurality of bags, and the structural support for the solar panels500 above the storage reservoir could be mounted in ground at the edgesof the bag that is the storage reservoir. If the storage reservoircomprises multiple bags, structural supports could be mounted betweenvarious bags that make up parts of the storage reservoir.

In regard to the discharge reservoir, it is possible that solar panels500 may be mounted so as to occupy at least some of the same land areaas the discharge reservoir, being located above the discharge reservoir.The solar panels 500 can be mounted on a fixed structure that isstructurally independent of the discharge reservoir. Such solar panelscould be fixed, single-axis tracking, or dual-axis tracking, or anyother desired configuration.

In regard to the discharge reservoir, the discharge reservoir could be abag or a plurality of bags, and the structural support for the solarpanels 500 above the discharge reservoir could be mounted in ground atthe edges of the bag that is the discharge reservoir. If the dischargereservoir comprises multiple bags, structural supports could be mountedbetween various bags that make up parts of the discharge reservoir.

In regard to the discharge reservoir, it is possible that the dischargereservoir could be an open body of water such as a lake. In such asituation, solar panels could be part of a construct that floats on thesurface of the body of water. Alternatively, the solar panels could bemounted on a structure that rests on or is anchored to the bottom of thebody of water. In any such situation, such solar panels could be fixed,single-axis tracking, or dual-axis tracking, or any other desiredconfiguration.

In regard to the storage reservoir, referring now to FIGS. 4A-4B, in anembodiment of the invention, there may be placed, atop the overburden,solar energy collectors or panels 500 that transmit at least part oftheir weight to the overburden 130. The weight of the solar energycollectors 500 contributes to the weight that is lifted to store energy.Electrical connections to the solar energy collectors or panels 500could be made by cables that are sufficiently flexible and areappropriately routed to accommodate the motion of the overburden 130during a charging-discharging cycle.

In an embodiment that combines pressurized pumped energy storage withsolar panels 500, the system may be constructed by installing the bagfor the storage reservoir, covering it with earth as overburden 130, andthen placing solar panels 500 on top of the repositioned earth oroverburden. As described elsewhere herein, the overburden 130 moves upand down as the bag 100 of the storage reservoir is filled and emptied.In addition to the vertical motion, it can be expected that portions ofthe overburden 130 may change their surface slope, especially near theedges of the bag 100. If the solar panels 500 are connected toindividual bases and the slope or orientation of the individual baseschange, this can in turn change the orientation of solar panels 500 thatare placed on top of the overburden 130. Such change of orientation candegrade the collection efficiency of the panels 500, as well as causingpossible structural support problems.

It is possible that the system for supporting the solar panels 500 maycomprise a tracking system such as a two-axis tracking system. It ispossible that such controls could serve to achieve desired orientationof the solar panels 500 relative to gravity and to a universalcoordinate system without the need to measure local orientation of thesurface of the overburden 130. It is possible that such controls couldmove the solar panel in whatever manner relative to its supportstructure is needed, regardless of the orientation of a particularsupport. Such a control system could use information such as GlobalPositioning System coordinates, time-of-day information, and otherinformation.

It is also possible that the system may comprise a tilt sensor orsensors on an individual solar panel 500 or structure or on a platform600 to which the solar panel 500 is connected. The controls that changethe orientation of an individual photovoltaic panel may be responsive tothe tilt sensor(s) and to other instructions so as to maintain theindividual photovoltaic panel in a desired orientation with respect to auniversal coordinate system or to the sun. The use of such sensors andcontrols is especially suitable if the tracking system is a two-axistracking system. Such adjustment could be achieved for individualphotovoltaic panels by appropriate software programming. If the supportstructure for a particular solar panel 500 changes its orientation, thecontrol system could compensate for that motion to maintain the desiredorientation of solar panel 500. For solar panels that are located in theinterior of the overburden region, where the surface of the overburden130 may remain close to horizontal during all parts of thecharge-discharge cycle, the controls might have only little differenceor no difference from the controls for a more conventionally mountedsolar panel whose support is rigidly mounted to ground. For solar panels500 that are located near the edge of the overburden region, moresophisticated controls or algorithms might be used to compensate for thechanging slope of the surface of the overburden.

As illustrated in FIG. 4, groups of several solar collectors 500 (asillustrated, four solar collectors 500) are mounted on an individualplatform 600, which in turn rests on a portion of the overburden.Individual platforms 600 may be connected to other individual platforms600 by connections that generally resist at least some relativedisplacement between the platforms 600 but do permit change of relativeangle of the platforms. The connections are illustrated as links ofchain, but of course other forms of connection are also possible.Individual platforms 600 may have individual orientations as a functionof the extent of filling of the bag 100. As illustrated, there iscontrol of the orientations of individual panels 500 by a trackingsystem that provides rotation of the panels 500 around two axes ofrotation 510A, 510B. Such orientation control may be responsive to tiltsensors or orientation sensors. Such sensors may be located in therespective platform or in the respective solar panels, or elsewhere.Accordingly, the tracking system may orient the solar panels 500 indesired orientations despite variations in slope of the surface ofoverburden or the orientation of platforms 600. The slope of the surfaceof the overburden 130 may vary from place to place in the overburden 130and as a function of time (or the extent of filling of the bag 100).

Alternatively, in embodiments of the invention, there may be provided asolar panel support system that comprises an orientation preservationsystem. For example, it may be desirable to maintain the orientation ofa central post that supports an individual solar panel 500 such that thecentral post remains vertical. Such an orientation preservation systemcan comprise linkages (bars that are hinged or pinned to other bars)that form parallelograms 700. Joints in the linkages may be by pinnedjoints or hinges, which allow the joint to rotate around one axis ofrotation, but constrain against all other types of motion. The sides ofthe parallelogram 700 may be bars or in general any rigid structures.

Parallelograms formed of such linkages can allow their sides to move incertain motions, while the parallelism of opposite sides is maintained.Thus, if one side of the parallelogram 700 is maintained vertical by ananchor that is mounted in fixed ground, then the opposite side of theparallelogram 700 always is vertical also. If a parallelogram 700 isjust a single parallelogram linkage, although parallelism of opposedsides is maintained, there is a constraint on horizontal distancebetween the sides that are maintained parallel. If there is verticalmotion of one of the parallel sides relative to its correspondingparallel side, then there is required to be a defined amount ofhorizontal motion. This might be undesirable for the presentapplication. Accordingly, it is possible to provide an orientationpreservation system that comprises two parallelograms 700 in series,connected so that they have one leg in common, which may be a verticallyoriented leg. For such pair of two parallelograms 700 in series, if oneedge of one parallelogram 700 is maintained vertical, then the last edgeof the last parallelogram 700 still always remains vertical also, whileat the same time having two parallelograms 700 in series allows forchange, in the horizontal direction, of distance between two posts. Atwo-parallelogram linkage allows an amount of horizontal translationthat is independent of motion in the vertical direction, while at thesame time allowing vertical translation of the distal vertical member ofthe linkage. It is also possible to provide a linkage in which one endof a linkage is able to slide along a vertical post and thereby maintainverticality of the opposite end of the linkage. Such a linkage can havebars that form an “X” with a central pivot point, and are connected toeach other with hinged joints at the ends of the bars.

There may be linkages, such as parallelogram linkages, in more than onedirection to a particular post of a solar panel support. Linkages mayconnect a particular post to anchor posts that are on stationary ground,or may connect a particular post of a solar panel to a post of anothersolar panel, or there may be a combination of such connections.

It is also possible that, because change in the orientation of theoverburden surface is expected to occur more significantly near the edgeof the installation and less in the interior of the installation, itmight not be necessary to provide the orientation preservation systemfor every solar panel 500. In such a situation, it is possible thatsolar panels 500 in the interior of the overburden region could bemounted to the overburden in a manner with no adjustment for possibletilting of the base, while solar panels 500 that are mounted near theedge of the overburden region could be provided with compensation fortilting of their bases. It is possible that such solar panels 500 in theinterior region could be rigidly connected to each other.

If a solar panel 500 comprises an orientation preservation system suchas the described linkages, it is possible that the solar panel 500 maybe connected to its base by a joint that allows one or more degrees ofrotation, such as a ball-and-socket joint.

Still further, if there are provided double-parallelogram linkages intwo different directions, such as two mutually perpendicular directions,it is possible to provide a pivotable joint, such as at the anchor post,to allow rotation of the linkage around a vertical axis such as theanchor post or a support post that supports a solar panel.

Use of Elevation Difference

In embodiments of the invention, the discharge reservoir could be at alower elevation than the storage reservoir. In such a situation,hydraulic head may come from a combination of pressure due to overburden130 on the bag 100, and hydraulic head due to elevation difference. Forexample, if the system is constructed by excavating and moving earth,and if the surface area of land from which earth is excavated is roughlythe same as the surface area of land that is covered by earth to formthe overburden on top of the storage bag, then the depth of theexcavation can be expected to be approximately the same as the height ofthe overburden 130. This is illustrated in FIG. 5A. Other elevationalrelationships are also possible. The discharge reservoir can be anotherbag, as illustrated in FIG. 5A, or alternatively it can be an open lake.

In FIG. 5A, the lightly dotted line indicates the original surface ofthe ground, assumed flat, before earthmoving. It is assumed that thestorage bag rests on that ground with a berm built up at the outer edgesof the storage bag to create a dish shape. It can be seen that at thestart of discharge when the upper bag is full, the pressure differenceor head available for energy generation is represented by the weight perunit area of the overburden, plus the pressure head of the water insidethe bag, plus the pressure head due to the distance below grade towhatever is the water level in the discharge reservoir. Some of thesequantities may change as a function of time during the dischargetransient.

Referring now to FIG. 5B, in still other embodiments of the invention,the discharge reservoir could be at an even lower elevation than whatmay be created by excavation of the soil needed to create theoverburden. For example, it is possible, depending on local topography,that some naturally occurring elevation difference might be available,and the discharge reservoir could be located at a somewhat lowerelevation than the storage reservoir. Such elevation difference need notbe as large as the hundreds of meters of elevation difference that aretypical of many conventional pumped storage hydro installations.Nevertheless, if some naturally occurring elevation difference isavailable, it would improve the economics of the installation by storingmore energy with little or no increase in the construction costs.

It is still further possible that the discharge reservoir could beunderground such as in an underground cavern. The discharge reservoircould be one volume of liquid or could be multiple volumes of liquid.

The discharge reservoir located underground could be an open-surfacebody of water located underground, essentially an underground lake, ifdesired. The discharge reservoir also could be a bag, if desired,although it might not be necessary to use a bag in such a situation.

In this situation of a discharge reservoir that is underground, placingthe overburden 130 on top of the storage reservoir bag would contributeto hydraulic head, but there would also be a significant amount ofhydraulic head already be available due to the distance by which thedischarge reservoir is placed underground.

In still other embodiments of the invention, there may be providedmultiple discharge reservoirs at various elevations. This is alsoillustrated in FIG. 5C. The surface areas of respective reservoirs candetermine how much the liquid levels of the respective reservoirs changeduring a discharge cycle. It is further possible that some of the liquidcould be in an open reservoir while other of the liquid could be insidea bag.

It has been illustrated in FIG. 5A that a discharge reservoir could bein the form of a bag that is located in a depression in the ground, thatis created by earthmoving or excavation in connection with providing theoverburden on top of the storage bag. Such excavation or earthmovingcould be accomplished, for example, by a bulldozer or similar piece ofequipment. However, such equipment is not the only possible way toprovide overburden and possible elevation difference. As illustrated inFIG. 5C, it would be possible to drill into the ground and possibly alsoexcavate at the bottom of the hole. Drilling and/or excavating couldprovide loose earth material that can become part of the overburden 130.Furthermore, drilling possibly followed by excavating can provide anamount of depth and elevation difference that is greater than what iseasily achievable by simple earthmoving at the surface of the earth. Ifa hole is drilled, it is further possible that a bag could be providedinside the drilled hole. It is not necessary that all of the storagevolume be created by drilling. It may be desirable to create only aportion of the storage volume by drilling and to create another portionof the storage volume by earthmoving or by access to an open body ofwater, which may be at a different elevation from storage volume that iscreated by drilling. Any combination of these can be used, and theycould be operated in any desired sequence. Each may provide a differentelevation or amount of elevation change during the process of going fromempty to full for that individual storage volume. If multiple storagevolumes are used each having its own pressure range, it may be possibleto provide an individual turbine or pump suited to the appropriatepressure range flowrate or other characteristics. Pump-turbine 650 isillustrated in FIGS. 5A-5C. If an underground cavern is created, itcould have a bag inside it but it does not have to.

Tethers

Referring now to FIGS. 6A-6B, in an embodiment of the invention, the bagmay comprise internal tethers. A tether 800A or 800B may be a flexiblemember that connects the upper layer 110 of the bag 100 with the lowerlayer 120 of the bag 100 and is capable of carrying tensile load. Thepresence of a tether or tethers can influence or constrain the shape ofthe bag when the bag is filled or partially filled. For example, if abag when filled tends toward a round or spherical shape, the presence oftethers in a middle region can constrain the bag to be flatter than itwould be without such tethers. A tether 800A or 800B can be a cord-likecomponent, or a plurality of cord-like components, or a web-like (sheetof fabric) component or a plurality of web-like components. Tethers 800can be attached to the lower layer 120 and upper layer 110 of the bag100 by stitches or by other means. FIG. 6A shows a tether 800A thatextends in a generally vertical direction when the bag is full or nearlyfull. Such tethers can create a depression in the upper layer of the bagnear their attachment points. This tether 800A is shown in FIG. 6A as aweb-like (sheet of fabric) type of tether, which could be disposed in aninterrupted manner. FIG. 6B shows tethers 800B that extend in diagonaldirections in a criss-cross manner when the bag is full or nearly full.Such tethers 800B would be capable of creating a local protrusion in thebag between attachment points of the tethers. These tethers 800B areshown in FIG. 6B as being individual cord-like tethers.

In an embodiment of the invention, in a cross-section, the upper layerof the bag does not have to have the same dimension as the lower layerof the bag. For example, the upper layer of the bag can be longer orwider than the lower layer of the bag. This may result in “wrinkles” inthe upper layer of the bag. Such “wrinkles” may have some impact on howthe overburden interacts with the upper layer of the bag as the upperlayer of the bag raises or lowers, and changes shape, during filling oremptying of the bag, and as the overburden displaces or changes shapeduring filling or emptying of the bag.

Further Comments

Where reference is made to water, it is equally possible to refer togenerally any liquid. Such liquid may, for example, be seawater. Suchliquid could be generally any aqueous liquid, or any liquid, subject ofcourse to economic considerations. Even more generally, it would bepossible to use any fluid, even a gas such as air.

The bag can be generally of any shape. One possibility of bag shape is ashape that is generally elongated, having a longitudinal axis. Thelength of the bag along the longitudinal axis can be longer than adimension of the bag in any other direction. In cross-sectionperpendicular to the longitudinal axis, the bag, when it is filled ornearly filled, can have a cross-sectional shape that repeats itselfalong the longitudinal axis for some distance. Such a bag could bedescribed as cylindrical or tubular (although it does not have to beround in cross-section). In such a bag, near the ends there could be aspecial geometry that is different from the geometry that repeats itselfin the main part of the bag. In other embodiments, the bag need not beso elongated as has just been described. In these other embodiments, inplan view, the bag could be round, square, square with rounded corners,rectangular, rectangular with rounded corners, or still other shape.

What is referred to as a reservoir, either a storage reservoir or adischarge reservoir, could in general be a plurality of reservoirs. In aplurality of reservoirs, the individual reservoirs could be of identicaldesign, size and elevation, or could be of different designs ordifferent sizes or different elevations, in any combination. In such asituation, plumbing and equipment could be provided to access theindividual reservoirs in any combination and in any sequence.

In embodiments of the invention, it is possible that the storage bagcould be located, with respect to neighboring terrain, either generallyabove the neighboring terrain, at approximately the same level as theneighboring terrain, or generally below the neighboring terrain. Any ofthese could be achieved by appropriate earthmoving or structure. Anunderground cavern could be a mine that is not in use, or a naturallyoccurring cavern, or a cavern created for the purpose. Any desiredstructure could be placed or constructed on top of the bag or on top ofthe overburden that overlies the bag. The same is true for the dischargebag.

What is referred to as a solar collector could be a photovoltaic solarenergy collector but could also be any other type of solar energycollector (thermal, mirror, etc.) that may be desired.

It is further possible that embodiments of the invention could be usedfor water storage in addition to or instead of for energy storage. Suchpurposes could include fire suppression, emergency response, municipalwater supply, and other purposes.

Embodiments of the invention can also include variations andcombinations of what has been disclosed, in any combination that isphysically possible. Although embodiments of the invention have beendisclosed, it is not desired to be limited thereby. The embodiments ofthe invention described above are intended to be merely exemplary;numerous variations and modifications will be apparent to those skilledin the art based on the disclosure. All such variations andmodifications are intended to be within the scope of the presentinvention as defined in any appended claims.

All referenced documents are incorporated herein by reference in theirentirety.

The following are some exemplary claims directed to the subject matterdescribed above and should not be considered to limit the presentinvention; applicant reserves the right to pursue claims to any of thedisclosed subject matter.

We claim:
 1. An energy or fluid storage system comprising: a substrate,said substrate having a substrate central region and, outward of andsurrounding said substrate central region, having a substratesurrounding region, said substrate central region having a concave shapewhen viewed from above, and said substrate surrounding region having aconvex shape when viewed from above, a bag comprising a deformableboundary defining an interior that can be filled with said fluid andemptied of said fluid as desired, wherein said bag comprises a lower baglayer overlying said substrate in both said substrate central region andsaid substrate surrounding region and comprises an upper bag layer abovesaid lower bag layer, said bag being capable of occupying a less-filledconfiguration and a more-filled configuration; and a mass of overburdenoverlying said upper bag layer, said mass being able to be raised andlowered as a function of an extent of filling of said interior of saidbag, wherein said lower bag layer overlying said substrate hassubstantially identical configuration in both said less-filledconfiguration and said more-filled configuration, wherein said upper baglayer, in said less-full configuration, in an upper bag layer centralregion, is concave when viewed from above and outward of said upper baglayer central region is convex when viewed from above, and wherein saidupper bag layer, in said more-filled configuration, in said upper baglayer central region, is convex when viewed from above, wherein saidinterior of said bag comprises an internal filler piece having alongitudinal direction that at least approximately extends along all orat least a portion of an outer perimeter of said bag, wherein saidinternal filler piece has a cross-sectional shape, said cross-sectionalshape being a shape of a cross-section taken perpendicular to saidlongitudinal direction of said internal filler piece, wherein saidcross-sectional shape has an outer radius of curvature at anouter-facing portion of said internal filler piece facing said outerperimeter of said bag, and has an inner radius of curvature at aninner-facing portion inward of said outer-facing portion, wherein saidinner radius of curvature is smaller than said outer radius ofcurvature, and wherein said upper bag layer is unattached to saidinternal filler piece.
 2. The system of claim 1, wherein saidcross-sectional shape of said internal filler piece has a maximumoverall horizontal dimension and a maximum overall vertical dimension,and said maximum overall horizontal dimension is greater than saidmaximum overall vertical dimension.
 3. The system of claim 1, whereinsaid internal filler piece has a maximum overall vertical dimension thatis at least two times a thickness of a material of which said bag ismade.
 4. The system of claim 1, wherein said outer radius of curvatureof said internal filler piece is at least one thickness of a material ofwhich said bag is made.
 5. The system of claim 1, wherein said innerradius of curvature of said internal filler piece is less than onethickness of a material of which said bag is made.
 6. The system ofclaim 1, wherein said inner radius of curvature of said internal fillerpiece is less than 0.2 of a thickness of a material of which said bag ismade.
 7. The system of claim 1, wherein said cross-sectional shape ofsaid internal filler piece is entirely convex.
 8. The system of claim 1,wherein said cross-sectional shape of said internal filler piece isconvex in some places and concave in some other places.
 9. The system ofclaim 1, wherein said cross-sectional shape of said internal fillerpiece tapers from a greater vertical dimension closer to said outerperimeter of said bag, to a smaller vertical dimension further inward.10. The system of claim 1, wherein said internal filler piece isattached to an interior surface of said bag.
 11. The system of claim 1,wherein said bag comprises at least one tether connecting said top layerand said bottom layer, said tether being capable of carrying tensileload.
 12. The system of claim 1, wherein material of said bag that is incontact with said internal filler piece is a single thickness of saidmaterial of said bag.